Hydro power systems are used for generating power from the tidal or current motion of water in oceans, bays, and rivers. Typically, such systems require a high water head and high flow conditions. System operating requirements that include both a larger water head and high flow conditions limit the suitable sites for locating fluid flow energy harvesters. Conventional hydro turbine technology, which involves positioning a powerhouse in a dam body with turbines located below the lowest water level, has been applied at mountain river and waterfall sites where a large water head can be developed. Consequently, powerhouses using hydro turbines are generally installed in large and complicated dam structures capable of withstanding the enormous water pressures generated. On the other hand, the hydro energy potential of thousands of rivers, streams, and canals remain untapped because hydro turbines, as an economical and practical matter, do not operate effectively with a low water head, in other words, when water level differences are about three meters or less. Such conventional hydro turbines need significant water depth for installation and cost-efficient operation.
Systems have also been developed to generate power using lower water head. These systems are described in U.S. Pat. Nos. 4,717,832, 5,074,710, and 5,222,833, the disclosures of which are incorporated herein by reference.
Systems for utilizing tidal motion and current flow of oceans and rivers are also known. Such systems usually require a dam or other physical structure that separates one part of a water body from another part. A difference in water levels is thereby created which provides a pressure differential useful for driving mechanical devices such as hydro turbine generators.
Also, axial-flow turbine type devices deriving power from liquid flow in tidal runs and stream beds are known. Such devices are disclosed in U.S. Pat. No. 3,980,894 to P. Vary et al., U.S. Pat. No. 3,986,787 to W. J. Mouton, Jr., U.S. Pat. No. 4,384,212 to J. M. Lapeyre, U.S. Pat. No. 4,412,417 to D. Dementhon, and U.S. Pat. No. 4,443,708 to J. M. Lapeyre.
Pivotal flow-modifying means is shown in the above Mouton, Jr. patent in a multiple unit embodiment.
U.S. Pat. No. 4,465,941 to E. M. Wilson discloses a water-wheel type device for the purpose of flow control pivotal valves or deflectors.
Additionally, various Magnus effect generating systems have been envisioned. The Magnus effect was first publicized by Professor G. Magnus in 1853. The Magnus effect is a physical phenomenon in which a spinning object creates a current of rotating fluid about itself. As the current passes over the object, the separation of the turbulent boundary layer of flow is delayed on the side of the object that moves in the direction of the fluid flow and is advanced on the side of the object that moves counter to the direction of the fluid flow. Thus, pressure is exerted in the direction of the side of the object that moves in the same direction of the fluid flow to provide movement substantially perpendicular to the direction of fluid flow. Briefly stated, when a rotating cylinder encounters a fluid flow at an angle to its rotational axis, a lifting force (lift) is created perpendicular to the flow direction. If a rotating cylinder is mounted on a vertical axis, the lift is developed at right angles to the direction of water flowing past the cylinder, left or right depending upon the direction of rotation.
The use of the Magnus effect as a windmill was disclosed in the 1926 translation of Anton Flettner, “The Story of the Rotor,” published by F. O. Willhofft, New York, N.Y. A Magnus rotor can produce ten times as much lift force as an airfoil for equal projected areas and wind speeds. The phenomenon is also used to describe, among other things, the curved pitches of baseball and the shooting of airplane guns transversely to the airplane's path of travel.
Various patents disclose the use of the Magnus effect for airplane lift, steering a boat, and for assisting in submarine steering.
The Magnus effect is utilized in U.S. Pat. No. 4,446,379 to Borg et al., which has Magnus cylinders mounted for rotation at right angles to shafts that are revolved about a generally vertical axis. The shafts are free to rotate 180 degrees. The Magnus cylinders are continuously rotated in the same angular direction. At one position of revolution of the shafts, the cylinders rotate on an axis generally parallel to the axis of revolution of the shafts. When the apparatus is immersed in a fluid flow (gaseous or liquid) a torque of rotation is developed when the shafts are aligned with the fluid flow, and this torque of rotation is reduced as the shaft approaches a position transverse to the fluid flow. As the shafts pass this transverse position, a torque is developed by the rotating cylinder that rotates the shafts 180 degrees at which point the formerly downwardly depending cylinder is now upright and the formerly upright cylinder is now downwardly depending on its shaft. The device was designed to utilize two or more shafts to which cylinders are attached, and there is continuous production of torque about the axis of revolution of the shafts. The complexity of this device makes it a difficult device to build or operate. If the Magnus effect is to be used to generate power, a simpler device is needed.
U.S. Pat. No. 4,582,013 to Holland describes a self-adjusting wind power machine that uses a Magnus rotor.
Pneumatically driven systems using turbine blades have also been developed. However, these systems normally use blades that rotate at high speeds. These rotating blades are problematic as any sizable foreign object encountered by the system can damage the blades, thereby compromising the structural integrity of the system. When the system utilizes the flow of air such as in the use of turbine blade aircraft, bird strikes can cause significant damage to the rotating blades, as can stones or other debris inadvertently or intentionally injected into the rotating blades. When the system is a water system, the injection of aquatic plants and animals as well as debris frequently found in waterways (e.g., chunks of wood) can also cause damage.
The majority of the systems envisioned by the aforementioned technologies utilize rotating blades that are noisy, detrimental to both flora and fauna, and require dams that interfere with the motion of the flowing water. Additionally, the systems that are utilized in these applications significantly obstruct sunlight, thereby detrimentally affecting aquatic plant life. These approaches are normally resisted by the affected communities due to the harm caused to flora and fauna and the damming of the body of water that negatively affects community activities. Damming and rerouting water flow can also cause significant upstream destruction of wildlife habitats.
Low head and low flow hydraulic conditions are prevalent throughout the world. The US Department of Energy (DOE) has studied the amount of low head water sources available in the United States and has published the result of that study in DOE report DOE-ID-11263 entitled Feasibility Assessment of the Water Energy Resources of the United States for New Low Power and Small Hydro Classes of Hydroelectric Plants. The difficulty described therein is that there are no simple and easy methods to harness the energy from low head water sources to create power.
Table 1 from that report provides a summary of hydroelectric energy in the United States and shows that with regard to the low head/high power and all low power sources including unconventional and microhydro sources, there is approximately 47,000 MW of power that is available for harvesting. Effectively harvesting this capacity would more than double the power currently generated by hydro sources in the United States alone.
Annual Mean Power (MW)TotalDevelopedExcludedAvailableTotal Power289,74135,42988,761165,551Total High Power229,79434,59676,864118,334High Head/High Power157,77233,42355,46468,885Low Head /High Power72,0221,17321,40049,449Total Low Power59,94783311,89747,217High Head/Low Power35,4033739,16325,868Low Head /Low Power24,5444612,73421,350Conventional Turbine8,4703198997,253Unconventional Turbine3,932435273,362Microhydro12,142991,30810,735
However, despite the technological efforts described previously there is no known system capable of generating electricity from low head/high power and low power sources such as tidal and/or river flow and being capable of continuous generation under changing flow conditions.
Given the increasing demand for industrial electricity in view of the issues related to the current state of the art of fluid flow energy harvesters, a need exists for a system that does not harm flora or fauna and can be introduced into the environment without interfering with the natural water flow or blocking the majority of the sunlight to the bottom of the body of water. A need also exists for an environmentally friendly, quiet, efficient, and simple energy harvester that can operate in low head and low flow conditions.